1. Field of the Invention
This invention relates to privacy screens and stereoscopic effects devices that use microprism sheets.
Each of the preferred embodiments of the invention has in common the transmission of light through a single microprism sheet made up of a transparent substrate in which are formed linear grooves having planar surfaces which intersect to form a v-shaped cross-section, the two sets of planar surfaces on respective sides of the grooves being selectively arranged to block or alter light transmitted through the sheet.
The microprism sheets used in the various preferred embodiments provide privacy screening and stereoscopic effects with an especially simple and low cost construction, and can easily be manufactured and/or assembled for use in a variety of applications.
The invention has three principal embodiments:
(i) The first principal embodiment relates to a privacy screen, and in particular to modification of a microprism sheet to emulate a privacy screen, to devices utilizing such privacy screen emulation arrangement, and to methods of making a privacy screen;
(ii) The second principal embodiment relates to stereoscopic image separation, and in particular to modification of a microprism sheet to separate interlaced images for the purpose of creating stereoscopic effects, to an arrangement utilizing such a stereoscopic microprism sheet, and to methods of making a stereoscopic microprism sheet;
(iii) The third principal embodiment relates to use of a microprism sheet to create interlaced images from separate sources such as a split screen, and which may be used in connection with the image separating arrangement of the second principal embodiment.
According to the first embodiment of the invention, a privacy screen is made up of a microprism transmission sheet. The microprism sheet of this embodiment is similar to the ones disclosed in U.S. Pat. No. 2,909,770 (Pugsley) and U.S. Pat. No. 4,756,603 (Ohtani) in that one of the two surfaces or facets of a microprism made up of v-shaped grooves is altered to attenuate or scatter light incident on the surface or facet, but instead of attenuating reflected light originating outside the image path, the modified microprism sheet of this embodiment of the invention attenuates or scatters light that would normally be within the optical path from the image source to a viewer situated in front of the microprism sheet, thereby providing a louvre or privacy screen effect.
According to the second embodiment of the invention, instead of preventing transmission of light through one of the surfaces or facets of an otherwise conventional microprism sheet, each of the two surfaces or facets of a microprism sheet made up of v-shaped grooves is modified to polarize light in an opposite direction. When the image source is an interlaced image, the oppositely polarized light may be recombined by corresponding polarized lenses to provide a stereoscopic effect. When a microprism sheet having a groove pitch corresponding to the pitch of the interlaced images is positioned over the interlaced images, the different sections of the interlaced image will be transmitted in different directions and oppositely polarized so that each lens will see a different channel for an enhanced three dimensional image.
According to the third embodiment of the invention, instead of altering the properties of light transmitted through the respective surfaces or facets of a microprism sheet made up of v-shaped grooves, the angles of the surfaces or facets on different portions of the microprism sheet are arranged so as to interlace separate images. This eliminates the need to interlace images during production, allowing the different portions of the image to be separately stored or transmitted and interlaced at the viewing end. Separation of the images for stereoscopic viewing can be in a conventional fashion using colored glasses or by means of the arrangement of the second principal embodiment of the invention.
2. Description of Related Art
Microprism sheets in the form of molded substrates with small prisms embedded within the material are well-known. The present invention involves various modifications or re-arrangements of a particular type of known microprism sheet in which a clear plastic material is formed with linear grooves, each having a v-shaped cross-section. Unlike prior devices involving multiple layers of microprism sheets, or microprism sheets combined with structures such as emicrolenses or light guides, each of the embodiments of the present invention utilizes a single microprism sheet, which may take the form of an overlay for a computer monitor or television, or which may be formed as an integral part of the monitor or television screen.
The prior art generally falls into one of two categories: (i) microprism sheets and devices using microprism sheets in which an image is uniformly transmitted through the microprism sheet, each facet of the microprism having identical light transmission properties and the facets being arranged in a uniform fashion across the sheet; and (ii) microprism sheets and devices utilizing microprism sheets in which one of the surfaces or facets of the microprisms in the sheet is altered in such a way as to reduce glare or reflections without affecting transmission of an image through the sheet.
The first category of prior art provides technical background concerning the materials and formation of microprism sheets and the manner in which light is transmitted through the sheets. Except as noted below, the materials and geometry of the sheets used in the preferred embodiments of the invention can easily be selected by those skilled in the art based on the principles disclosed in these patents, once the overall concepts of privacy screen emulation and image separation or interlacing are understood.
Examples of patents directed to microprism sheets in general, and to devices using microprism sheets, include the following: U.S. Pat. No. 5,836,096 (Brauer), U.S. Pat. No. 5,446,594 (Nelson et al.), U.S. Pat. No. 5,363,237 (Wakatake), U.S. Pat. No. 5,316,359 (Lansinger), U.S. Pat. No. 5,208,620 (Mitsutake et al.), U.S. Pat. No. 4,708,435 (Yata et al.) , U.S. Pat. No. 4,309,074 (Granieri), U.S. Pat. No. 4,309,073 (Nishimura et al.), U.S. Pat. No. 3,902,787 (Sherlock), and U.S. Pat. No. 4,206,969 (Cobb et al.) Each of these patents discloses transmission or projection devices that utilize microprism or Fresnel structures for the purpose of glare reduction or optimizing light transmission at all potential viewing angles. Also of general background interest is the transmission screen disclosed in U.S. Pat. No. 5,317,405, which uses Fresnel microprism structures to transmit an image from a television while at the same time reflecting an image of the viewer to a camera, and U.S. Pat. Nos. 5,835,661, 5,926, 601, and 5,359,691, all to Tai et al., which relate to light guide structures using microprisms. None of these patents discloses alteration of selected facets or surfaces in different intersecting planes to emulate a privacy screen or separate images according to the principles of the first and second embodiments of the present invention, or the arrangement of the planes to interlace images according to the principles of the third embodiment of the present invention.
U.S. Pat. No. 5,512,219 is of interest for its general disclosure of methods of making microprism sheets by casting, while U.S. Pat. No. 3,718,078 (Plummer) is of interest for its description of the use of acid etching for the purpose of creating light diffusing surfaces for non-glare glass and for focusing screens for cameras (xe2x80x9cfocusing screensxe2x80x9d are reflective surfaces used in cameras as disclosed in U.S. Pat. No. 3,971,051 (Ruhle)). In addition, U.S. Pat. No. 5,837,346 is of interest for its description of methods of making xe2x80x9cbulk diffusion screens,xe2x80x9d which may configured for collimation xe2x80x9cafter the fashion of Fresnel lensesxe2x80x9d and in which surface relief features may be formed by hot or cold embossing, by casting, or in any other way, and which may include reflective rear coatings formed by a particulate deposition process for use in front projection screens, or diffusion patterns created by photopolymerization. Those skilled in the art will appreciate that many of the methods of making or altering microprism sheets disclosed in these patents may also be used in making the microprism sheets of the preferred embodiments of the invention, and that the invention in its broadest form is not intended to be limited to any particular method of making or altering the sheets.
The second category of prior art includes U.S. Pat. No. 2,909,770 (Pugsley), U.S. Pat. No. 4,756,603 (Ohtani), and U.S. Pat. No. 4,165,920(Brown) , which describe arrangements in which one of the facets or surfaces of a microprism or Fresnel structure is altered by providing a light blocking or coating or treatment. These patents are most relevant to the first and second embodiments of the invention, in which a microprism sheet having linear grooves with a v-shaped cross-section is modified by altering the light transmission properties of at least one of the surfaces of each groove by attenuating or scattering light emitted in one direction. In particular, these patents describe the inclusion of light absorbing or scattering coatings or structures on selected microprism facets or surfaces, although they do not specifically suggest the use of such coatings or structures for the purpose of emulating a privacy screen, i.e., for altering the transmission properties of one of the surfaces or, facets relative to another, or for the purpose of separating an image into components that can be re-combined to form a stereoscopic image.
To the contrary, where image transmission is of concern in these patents, the microprisms tend to be arranged to increase the angles at which an image transmitted through the sheet is visible, even while limiting glare or reflections. Unlike the privacy screens of the first preferred embodiment of the invention, the glare reduction sheets disclosed in these patents seek to block only externally or internally reflected light and not to affect transmission of the image, whereas in the first embodiment of the invention, light is blocked in the path of the image to a viewer situated at a normal viewing angle. The privacy screens or stereoscopic imaging sheets of the invention, while superficially similar in structure to those used in the various embodiments of the present invention, are thus not to be confused with the glare reduction screens disclosed in this second category of patents, including the ones disclosed in U.S. Pat. No. 2,909,770 (Pugsley), U.S. Pat. No. 4,756,603 (Ohtani), and U.S. Pat. No. 4,165,920 (Brown).
The different functions of the prior microprism sheets having treated surfaces or facets manifest themselves in the different angles and arrangement of the microprism surfaces relative to those of the present invention. For example, U.S. Pat. No. 2,909,770 (Pugsley) discloses a transmission screen for a projection television receiver, slide projector, or the like, in which a microprism-like structure includes two surfaces, one of which is oriented at a 45xc2x0 angle so that light incident in the viewing direction is reflected away from the viewer, and the other of which is oriented parallel to the light transmission path so that it does not affect light transmission. To prevent multiple refractions and reflections of light off the microprism structure, the parallel (or xe2x80x9chorizontalxe2x80x9d) surface of Pugsley is xe2x80x9ccoated with a black or light-absorbent substance 6, such, for example, as dull black paint.xe2x80x9d Because of its parallel orientation, the coated surface of Pugsley, even though similar to that of the invention, does not serve as a privacy screen, but rather is arranged so as to maximize absorption of reflected light and minimize absorption of transmitted light.
Similar glare or reflection suppressing transmission screen arrangements are disclosed in U.S. Pat. No. 4,756,603 (Ohtani) and U.S. Pat. No. 4,165,920 (Brown). However, the arrangement of Brown is even less suitable than that of Pugsley for use as a privacy screen since Brown only coats a portion of the facets with an opaque material, while Ohtani discloses equally preferred alternatives involving treatment of a portion of the facets or the entire facets to reduce reflections, demonstrating a lack of concern or recognition of the potential to use the methods disclosed therein for privacy screening purposes. On the other hand, the Ohtani patent is of particular interest because, instead of coating the facets, the facets are altered by forming irregularities in the horizontal plane or at the peaks of the facets, the formation of irregularities being one of the methods that can be utilized to achieve the privacy screen of the first preferred embodiment of the invention
Similar glare reduction principles have also been applied to front projection screens, in which an image is projected onto the screen. For example, the structure disclosed in U.S. Pat. No. 4,911,529 (Van De Ven), includes a rear side reflective Fresnel or microlens structure and a front side Fresnel structure. Again, however, the facets of the front side Fresnel structure that are coated with a light absorbing material are parallel or xe2x80x9chorizontalxe2x80x9d facets rather than facets or surfaces through which the image would normally be transmitted to a viewer, and thus Van De Ven does not suggest a privacy screen effect, the purpose of the arrangement of Van De Ven being to prevent reflection of off-axis light that would blur the reflected image.
In general, the light absorbing materials used in the transmission screens of these patents must be placed on facets oriented perpendicular to the viewer, or to the image transmission path, so that they do not interfere with transmission or reflection of the image. The purpose of the transmission screen overlays of Pugsley, Ohtani, and Van De Van is essentially to optimize transmission or reflection of the image while suppressing ambient light that does not contribute to the image. Thus, even though microprism sheets are widely available and well-known, they have previously only been used in antiglare arrangements or in relatively complex light guiding or focusing devices. The possibility of modifying microprism sheets to form privacy screens or to separate an image to obtain a stereoscopic effect, or of arranging the sheets to interlace images, has not previously been recognized. There is no known prior art involving the use of microprism sheets as privacy screens, or to separate or interlace images for the purpose of creating stereoscopic effects.
Finally, those skilled in the art will appreciate that the microprism privacy screen of the first preferred embodiment of the invention could possibly be used in applications other than those involving television or computer displays, such as in applications involving light collection rather than image transmission. In this regard, U.S. Pat. No. 5,729,387 is of interest for its disclosure of the use of microprism sheets for light focusing purposes in a solar lighting apparatus, although this patent does not disclose or suggest any sort of privacy screen or louvre effect.
It is accordingly a first objective of the invention to extend the range of applications for microprism sheets to include a simple and inexpensive privacy screen, an image separating screen suitable for creating stereoscopic images, and an image interlacing screen also suitable for use in creating stereoscopic images, by modifying a standard microprism sheet of the type having a plurality of v-shaped grooves, to
a) alter the transmission properties of at least one surface of each groove in such a manner that light transmitted in different directions has different properties and thereby
a1) create a privacy screen by attenuating light in one plane and not in the second plane, or
a2) separate interlaced images for a stereoscopic effect by altering polarizations in the two planes, or
b) by arranging the standard sheet to have transmission angles which cause interlacing of images from separate sources, the interlaced images being useable to create a stereoscopic effect.
It is a second objective of the invention to provide a privacy screen that is simple to manufacture and that can easily be applied to a computer display or television so as to limit viewing of a displayed image to persons situated at a particular angle relative to the display or television.
It is a third objective of the invention to provide a simple and inexpensive privacy screen that can easily be applied to a computer display or television so as to selectively reveal portions of a displayed image to different viewers situated at different positions in front of the display or television.
It is a fourth objective of the invention to provide novel applications for microprism sheets arranged to emulate a privacy screen, and to provide various methods of making such privacy screen emulating microprism sheets.
It is a fifth objective of the invention to provide a simple and inexpensive device for separating images into components that can be recombined by lenses or glasses to form a stereoscopic image, and to provide methods of making such sheets.
It is a sixth objective of the invention to arrange standard microprism sheets in such a manner that they interlace images from separate sources to create an interlaced image suitable for stereoscopic viewing or to provide various other visual effects.
These objectives are achieved, according to a first preferred embodiment of the invention, by modifying a microprism sheet of the above-described type, i.e., a microprism sheet having substantially linear, v-shaped grooves, so that one of the intersecting surfaces attenuates or scatters transmitted light, thereby forming a privacy screen which permits viewing of an image in the direction of the untreated surface and prevents viewing of the image through the treated surface. The microprism sheet may be used either as a screen overlay to prevent persons from viewing the image who are not positioned directly in front of or at a specific angle relative to the screen, or in the form of a dual screen overlay to permit two persons to view different portions of an image displayed on a single screen.
Because of its simplicity and low cost, the privacy screens of this embodiment of the invention can be used in a wide variety of novel applications, such as to provide a screen overlay for two-player gaming applications. In such applications, the privacy screen blocks portions of an image in selected directions so that each player sees a different image.
The objectives of the invention are further achieved, according to a second preferred embodiment of the present invention, by modifying a microprism sheet of the above type so that one of the surfaces is polarized in a first direction and the other surface is polarized in the opposite direction, thereby providing a sheet in which light exiting the sheet in different directions is oppositely polarized. The angle at which the light is caused to exit the sheet is such that an interlaced image, when viewed by appropriately spaced lenses or eyeglasses, will be separated to obtain a stereoscopic effect. The microprism sheet of this embodiment may also be used as a screen overlay.
The objectives of the invention are also achieved, in accordance with a third preferred embodiment of the invention, by providing a microprism sheet having one set of surfaces oriented at a first angle corresponding to a position of a first image source, and a second set of surfaces oriented at a second angle corresponding to a position of a second image source so as to interlace the images. By appropriately selecting the first and second angles, the interlaced images can be made to project into the same plane for stereoscopic viewing using the arrangement of the second preferred embodiment, or into separate planes to provide a pseudo-stereoscopic effect without the need for additional lenses. Alternatively, if the images are pre-polarized or otherwise differentiated at the source, the interlaced images can be directly combined to exhibit a three-dimensional stereoscopic effect when viewed directly through corresponding lenses, or even, for appropriately recorded first and second images, combined for true stereoscopic viewing without the need for special lenses.
In each of the embodiments of the invention involving treated surfaces, whether for purposes of creating a privacy screen or for creating a stereoscopic effect, the surfaces may be treated by coating, delustering, chemical or laser etching, or casting. In the case of chemical or laser etching, surfaces may be made opaque by roughening, either by applying the chemical or directing the laser at he surface through an appropriate mask, or by etching the casting tool or die that forms the sheet. Alternatively, surfaces cast with texturing or a satin finish may be differentially polished to transmit light in the desired direction.
According to yet another aspect of the invention, the planes of the sheet that form the privacy screen could be provided with a visible pattern, for example through the use of colors, so as to form an image to provide a message, advertisement, or the like.